A vehicle is provided with a battery as a power supply, and an engine ECU, a starter motor, an alternator generator, etc. are connected to the positive electrode of the battery by way of fuses, respectively. In this case, the engine ECU, the starter motor, the alternator generator, etc. are divided into several groups according to their uses, and are connected to the battery by way of their respective power lines for exclusive use. Therefore, in a case in which communications are carried out using power lines, it is possible to construct a communication path by using a plurality of power lines, rather than to construct a communication path by using only a single power line.
In this case, as shown in patent reference 1, if communications are carried out in a common mode in which each load is connected between a power line and a chassis ground, the radiation power from the power line becomes large, though the wiring can be formed easily at a low cost.
Furthermore, as shown in patent reference 2, in a differential mode in which each load is connected between two power lines, the radiation power caused by power line communications can be further reduced compared with communications in the common mode.
[Patent reference 1] JP,2004-343796,A
[Patent reference 2] JP,2005-269513,A
Conventional power line communications include communications in the common mode and communications in the differential mode. Even when communications in either of the two different modes are carried out, if a plurality of power lines connected to a single battery are used for the communications, conduction noise is transmitted between the power lines and the communication quality is degraded.
The present invention is made in order to solve the above-mentioned problem, and it is therefore an object of the present invention to provide a power line communication apparatus which can prevent conduction noise from propagating between power lines, and which can carry out proper communications at a high speed.